Meperidine

Introduction


Meperidine, also known as pethidine, is a synthetic opioid agonist with distinct pharmacological properties. This article explores the pharmacology, pharmacokinetics, and side effects of meperidine.

Table 1: Characteristics of Meperidine

Characteristic Description
Structure Derived from phenylepiperidine
Receptor Affinity Acts on µ (m) and κ (k) opioid receptors
Chemical Structure Contains tertiary amine, ester group, and lipophilic phenyl group
Intrathecal Use Blocks sodium channels, suitable for intrathecal use
Similarity to Atropine Possesses mild atropine-like antispasmodic effect

Table 2: Pharmacokinetic Parameters of Meperidine

Parameter Description
Potency Compared to Morphine About one-tenth as potent as morphine
Duration of Action Shorter acting, lasting 2 to 4 hours
Equivalent Effects to Morphine Produces equivalent sedation, euphoria, nausea, vomiting, and respiratory depression
Absorption Absorbed from the gastrointestinal tract
Oral Usefulness Limited due to extensive first-pass hepatic metabolism (up to 80%)

Table 3: Metabolism of Meperidine

  Description
Hepatic Metabolism Extensive hepatic metabolism, including demethylation to normeperidine and hydrolysis to meperidinic acid
Elimination Primarily via urinary excretion (pH-dependent)
Normeperidine Active metabolite with an elimination half-time of 15 hours (35 hours in renal failure)
Accumulation Risk Prolonged administration can lead to normeperidine accumulation

Table 4: Clinical Uses of Meperidine

Clinical Use Description
Intrathecal Use Suitable for intrathecal administration for surgical anesthesia due to sodium channel blocking properties
Antishivering Effects Effective in suppressing postoperative shivering, possibly through k receptor stimulation
Delirium and Seizures May occur with prolonged administration, attributed to normeperidine accumulation
Serotonin Syndrome Risk when administered with antidepressant drugs that increase serotonin levels

Table 5: Side Effects of Meperidine

Side Effect Description
Cardiac Effects Modest atropine-like qualities, may increase heart rate
Myoclonus and Seizures Risk of normeperidine toxicity with prolonged use
Serotonin Syndrome Autonomic instability, confusion, agitation, hyperthermia, hyperreflexia when combined with certain antidepressants
Ventilatory Depression Can be more pronounced than morphine
Neonatal Exposure Rapid placental transfer, potential for neonatal exposure
Constipation and Urinary Retention May be less severe than morphine
Ophthalmic Effects Tends to cause mydriasis, dry mouth, and increased heart rate
Withdrawal Symptoms Different pattern from morphine, quicker onset, shorter duration

Conclusion
Meperidine, a synthetic opioid agonist, has unique characteristics and clinical uses, including intrathecal administration for surgical anesthesia and antishivering effects. However, its side effects and potential for normeperidine accumulation require careful consideration in clinical practice. Understanding its pharmacology and pharmacokinetics is essential for safe and effective use.

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